By design, detersive surfactants, generally present in excess in products such as shampoos, body washes, liquid soaps, laundry detergents, and toothpastes are meant to remove dirt, oil, grease, and particulate matter from the hair, skin, fabric, and teeth. Nonetheless, it is desirable that one or more hydrophobic or oil-based functional materials, called herein “benefit agent” or “active”, contained in these cleansing products, can be deposited and retained at relatively high levels on the substrates being cleaned, while not sacrificing detergency and foaming properties of these products. These actives, having benefits related to hair-care or skin-care or fabric-care or dental-care may range from silicones used as hair-conditioning agents, to emollient oils and fragrance used as skin-moisturizing and aesthetic or sensory property-boosting agents. The majority of these benefit agents tend to be expensive, and hence may be included in the detersive products only at relatively low to moderate levels. Adequate deposition and retention of the benefit agents on the hair, skin, fabric, and teeth, therefore, is critical to achieving the positive effects of these actives, when they are to be delivered through products like shampoos, liquid soaps, laundry detergents, and toothpastes.
The prior art includes numerous patents describing methods for improving the deposition of different hydrophobic or oily actives from detersive compositions. Majority of these reported inventions, for example, the ones described in U.S. Pat. Nos. 3,723,325, 5,085,857, 5,500,152, 5,543,074, 5,776,443, 5,853,707, 5,990,059, 5,935,561, 5,923,203, 6,126,954, 6,156,713, 6,277,361 B1, 6,436,383 B2, 6,706,258 B1, U.S. patent application 2005/0158266, and WO 98/11869 involve the use of certain polymeric materials, many of which are generally referred to as deposition polymers, comprised of various types of cationic polymer-based additives. Despite the large number of patents disclosing cationic polymer-aided methods for enhancing the deposition of benefit agents from surfactant-laden products, there is a need for substantially improving the deposition efficiency. The trends in consumer preference related to detersive hair-care products, like shampoos, illustrate this void. Most 2-in-1 shampoos (the conditioning shampoos) in the market utilize cationic polymers for enhancing silicone-deposition on the hair in order to provide for hair-conditioning. Yet, most consumers who seek high levels of hair-conditioning prefer conditioners, the non-detersive hair-conditioning products, to the detersive products like the 2-in-1 shampoos. A likely reason for this might be that with the 2-in-1 shampoos, a considerable amount of the hair-conditioning agent, silicone, is rinsed away during shampooing, despite the deposition polymer contained therein.
In light of the distinguishing features of the present invention over the prior art, it appears that one plausible cause for the inadequate performance of the cationic deposition polymers as used in the prior art is that these polymers and the benefit agents are added as separate ingredients in producing the final detersive compositions, i.e., the deposition polymer(s) is not adsorbed onto the benefit agent(s) as these ingredients are incorporated into the final compositions. Nonetheless, in order for the cationic polymer to function adequately as the deposition-aid, it must first attach onto the benefit agent. Given that all cleansing products contain relatively high loadings of anionic surfactants, and in contrast, relatively low levels of the benefit agent(s) and the deposition polymer, adequate binding of the deposition polymer onto the benefit agent may not be possible when these ingredients are added separately to the detersive compositions. It is speculated herein that the underlying reasons might be the following:    i) factors such as high concentration of anionic surfactants, and strong interaction (electrostatic) between an anionic surfactant and a cationic polymer are likely to favor association between the anionic surfactants and the cationic polymer over that between two weakly interacting, low-level ingredients, the cationic polymer and the hydrophobic benefit agent, especially considering that the commonly used cationic deposition polymers (for example, cationic cellulose and guar derivatives) are mostly hydrophilic polymers;    ii) since the amount of anionic surfactant likely to adsorb on the benefit agent would be much smaller than the amount of anionic surfactant remaining unadsorbed, the cationic deposition polymer is more likely to (associate) form complexes with the unadsorbed surfactant molecules rather than with the adsorbed surfactant molecules;    iii) being present at a much higher concentration than any cationic polymer-anionic surfactant complex that could possibly form, and having a diffusivity much higher than that of such a complex, the anionic surfactants might adsorb on the hydrophobic benefit agent far more easily than the polymer-surfactant complex; and    iv) the hydrophobic benefit agent may simply dissolve in the surfactant-rich solution.
In fact, it is often theorized in the art that association between the cationic deposition polymer and the benefit agent is achieved only when the cleansing products get heavily diluted during the course of the rinsing process. Clearly, large portions of the added deposition polymer and the benefit agent would be rinsed off before this optimum dilution level is reached.
Albeit, the prior art reveals approaches other than the use of cationic deposition polymers, for example, as disclosed in the U.S. Pat. Nos. 5,726,138, 6,541,565 B2, and 6,667,029 B2, the commercial detersive products continue to rely on these polymers for the deposition of hydrophobic or oil-based benefit agents. This might be because the deposition polymer-free approaches are not commercially viable from the standpoint of cost, product stability, and bulk manufacturing.
The prior art also includes approaches where droplets of hydrophobic benefit agents are encapsulated within a capsule comprising a complex coacervate of a polycation and a polyanion, as disclosed in WO 98/11870. The encapsulated droplets have a particle size distribution such that at least 10% by weight of the droplets comprises relatively large particles having a diameter of at least 100 microns. As noted in WO 98/11870, the efficacy of the claimed compositions relies heavily on parameters such as the relative hardness/softness and the thickness of the complex coacervate, as well as the size of the droplets of hydrophobic benefit agents, which would be hard to control in a cost-effective manner, especially during bulk manufacturing. The above approach presents additional limitations: i) encapsulation of a hydrophobic agent within a capsule comprising a complex coacervate would limit realizing the benefits which could have been derived otherwise from bare (non-encapsulated) hydrophobic benefit agents (for example, fragrance emission, and hair conditioning requiring direct deposition of silicone on the hair shaft); and ii) on account of having relatively large sized droplets of the hydrophobic benefit agents in the aforementioned compositions, attaining good product stability might be difficult, while attaining merely modest stability would invariably require viscous product forms, limiting severely the scope of varying the product consistency, which in turn might be undesirable from the standpoint of product aesthetics and ease of manufacturing.
It is therefore an object of the compositions and methods described herein to provide a more efficient method than the methods described in the prior art, for the deposition and retention of hydrophobic or oil-based benefit agents from detersive compositions. It is a further object that the compositions and methods are relatively inexpensive, involves manufacturing steps that are easy to implement or control, and do not adversely affect the stability, detergency, and foaming properties of the cleansing products. A related object is to provide stable, low-cost, detersive compositions that allow significantly high deposition and retention of hydrophobic benefit agents onto substrates including the hair, skin, and fabric.
Furthermore, it would be highly convenient to have the hydrophobic benefit agents available in a form which can be incorporated easily into a final product composition. In that vein, it would be of much benefit, if such an additive-form for the benefit agent also served towards attaining an enhanced deposition of the benefit agent. Nonetheless, a critical issue to be addressed in producing this additive-form is its long-term storage stability. It is therefore a further object of the compositions and methods to provide a highly stable additive-form for the hydrophobic benefit agents, which, when incorporated into detersive compositions, leads to an increased deposition of the benefit agents.
Several of the patents cited above, for example, U.S. Pat. No. 6,706,258 B1, describe the use of preformed oil-in-water (O/W) emulsions of hydrophobic benefit agents, wherein the oil-phase containing the benefit agent, is emulsified using (anionic, nonionic) surfactant-based emulsifiers. However, in the reported inventions, wherein a cationic polymer-based additive was used in conjunction with a preformed emulsion of a hydrophobic benefit agent (or a hydrophobic benefit agent alone), the cationic polymer-based additive and the preformed emulsion (or a hydrophobic benefit agent alone) were incorporated into the final detersive composition as separately-added ingredients, i.e., no attempt was made therein to pre-adsorb the cationic polymer-based additive onto the emulsion droplets (or the hydrophobic benefit agent) and subsequently adding the polymeric additive-modified emulsion (or the hydrophobic benefit agent) as a composite ingredient in producing the final detersive composition. In fact, there is no known prior art document wherein a cationic polymer-based additive was used as part of the emulsifier system used to produce an O/W emulsion of a hydrophobic benefit agent, that is subsequently incorporated into a detersive composition, with the detersive composition exhibiting enhanced deposition of the hydrophobic benefit agent onto an intended site during use, along with good stability, and minimal detrimental effect on detergency and foaming properties, as in accordance with the compositions and methods described herein.